Desulfurization of fluid coke with sulfur dioxide containing gas



United States 2,739,l@5 Patented Mar. 20, 1956 fice DESULFURIZATION F FLUID CGKE WITH SULFUR DIOXIDE CONTAINING GAS Francis P. Ford and Joseph F. Nelson, Westfield, N. 1., assignors to Esso Research and Engineering ompany, a corporation of Delaware No Drawing. Application September 13, 1954, Serial No. 455,778

7 Claims. (Cl. 202-31) This invention relates to improvements in desulfurizing and increasing the density of coke particles containing high percentages of sulfur. More particularly, it relates to an eflicient high yield desulfurization of petroleum coke particles from the fluid coking process by subjecting the coke particles to treatment at elevated temperatures with a sulfur dioxide containing gas whereby the sulfur content of the coke is reduced and its density increased.

There has recently been developed an improved process known as the fluid coking process for the production of fluid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. In a typical operation the heavy oil to be processed is injected into the reaction vessel where it comes in intimate contact with a dense, turbulent, fluidized bed of hot inert solid particles, preferably coke particles. Staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects rapid distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the heater or burner vessel. A stream of coke is transferred from the reactor usually to a separate heater or burner vessel employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Sufficient coke or other carbonaceous matter is burned in the burning vessel with an oxygen-containing gas to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About of coke, based on the feed, is normally burned for this purpose. This may amount to approximately to of the coke made in the process. The unburned portion of the coke represents the net coke formed in the process and is withdrawn. Alternately, heat may be supplied to the heater or burner section by introduction of preheated gases or solids in which case a higher yield of coke is obtained.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy or reduced crudes, vacuum bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically such feeds can have an initial boiling point of about 700 F. or higher, an A. P. I. gravity of about 0 to 20, and a Conradsorn carbon residue content of about 5 to wt. percent.

2 (As to Conradson carbon residue see ASTM Test D-180-52.)

It is preferred to operate with solids having a particle size ranging between 100 and 1000 microns in diameter with a preferred average particle size range between 150 and 400 microns. Preferably not more than5% has a particle size below about microns, since small particles tend to agglomerate or are swept out of the system with the gases. The withdrawn product coke has a diameter predominantly in the range of about 20 to mesh.

The method of fluid solids circulation described above is Well known in the prior art. Solids handling technique is described broadly in Packie Patent 2,589,124, issued March 11, 1952.

Fluid coking has its greatest utility in upgrading the quality of heavy petroleum oils, i. e., low grade petroieurn vacuum residua and pitches, from highly asphaltic and sour crudes. Such rcsidua frequently contain high concentrations of sulfur, i. e. 3 wt. percent or more, and the coke product produced from these high sulfur feeds are also high in sulfur content. In general the sulfur content of the coke product from the fluid coking process is about 2 times the sulfur content of the residuum feed from which it is produced. The sulfur content of coke from sour residue can range from 4 to 12 Wt. percent sulfur or more.

The high sulfur content of the coke product poses a major problem in its efficient utilization. For most nonfuel or premium fuel uses a low sulfur content coke, about or below 4 wt. percent sulfur, is required. For example, low sulfur content coke is desired for the manufacture of phosphorous, for the production of calcium carbide, for lime burning in the manufacture of soda ash or other alkalis, for various metallurgical applications, for the production of electrode carbon for various electrochemical applications such as the manufacture of aluminum and the like. In the case of electrode carbon it is desired to have a maximum of about 3% sulfur, preferably 2% or even less. The lower the sulfur content the better, since sulfur attacks the metal components of the electrode and in the form of sulfur dioxide it contaminates the efiluent gases. In particular iron sulfide is formed from the attack on the electrode iron components, which introduces highly undesirably iron into the aluminum.

In addition the real density of the fluid coke is about 1.5, which is below the figure of about 1.9 required for some specialty applications. The increasing of the density and the lowering of the sulfur and volatile content is particularly necessary before the fluid coke is suitable for manufacture into electrodes, one of the major uses of petroleum coke.

The conventional methods of reducing the sulfur content of coke from ordinary sources with gaseous reagents have in general not been too satisfactory. The results are even poorer when these procedures are applied to fluid coke. Fluid coke is laminar in structure and may comprise some 30 to 100 superposed layers of coke. Consequently, it is difficult for a reagent to penetrate more than a few outer layers. These difliculties inherent in fluid coke are even further compounded because of the beforementioned possibly higher than normal sulfur content of the coke derived from high sulfur petroleum feeds.

In one of the preferred conventional methods, the sulfur content of coke has been decreased and its density increased by calcination at temperatures above 2000 F. with various gases, principally air. The time required for effective desulfurization is however quite often inconsistent with good yields of the coke as the latter is consumed during the operation. Consequently, this makes the calcination operation relatively expensive.

This invention provides an improved process for lowering the sulfur concentration of fluid coke. The process comprises subjecting the high sulfur-containing fluid coke to treatment at elevated temperatures with a sulfur dioxide-containing gas whereby the sulfur content of coke is reduced and its real density increased.

It is surprising to find that a gaseous sulfur-containing compound should be effective in so reducing the sulfur content. It is especially surprising to find that sulfur dioxide is the most effective gas of the many tried for the reduction of the sulfur content of the fluid coke.

The conditions of the treatment are listed below. The temperature utilized is in the range of 2000 to 2900 F., preferably about 2200 to 2700 F.; the pressure utilized is generally in the range of to about 75 p. s. i. g., although the exact pressure is relatively unimportant compared to the temperature.

The time interval utilized depends on the temperature and pressure but is in the range of'15 minutes to 6 hours, and preferably 30 min. to 4 hours. The higher the temperature the lower the time interval.

The mole percent concentration of sulfur dioxide in the treating gas is in the range of 1% to 100%, preferably about 5% to 100% with to 6000 v./v./hr., preferably to 3000 v./v./hr. It should be recognized, however, that the v./v./hr. of the treating gas can vary over wide ranges. The rates given are merely indicative. The rate depends on the amount of sulfur dioxide in the treating gas, the temperature, the sulfur content of the original coke and the degree of desulfurization desired. The sulfur dioxide containing gas can be obtained by burning organic material containing appreciable sulfur. Other sources of sulfur dioxide include the pure gas. Diluent gases that can be employed include preferably nitrogen and carbon monoxide, although air, carbon dioxide, etc. may be used.

The sulfur dioxide treatment of the fluid coke can be conducted while the latter is in the form of a dense, turbulent, fluidized bed, a moving bed, or a fixed bed, usually depending on the equipment available.

The following examples further show the advantages of this invention.

EXAMPLE 1 Similar samples of high sulfur, i. e., 6.5 to 7.6 wt. percent sulfur, coke having a real density of about 1.5 were treated with a large number of different gases at 2400 F. for time intervals of from 10 to 60 minutes. About 140 g. of coke were treated at a rate of 2 liter per minute or about 1000 v./v./hr. in a fluid system.

These runs were discontinued for the most part after 30 minutes because time intervals of that nature have been found to be valid and reliable in screening tests on different gaseous materials. Varying the temperature or time of treatment or both within the prescribed ranges can bring the sulfur content down to the levels required.

The results are presented below:

Treat Real 101d Density Sulfur S02 20% S02, 80% N These results show that the lowest overall sulfur content and the hi' hest density were obtained with the use of sulfur dioxide exclusively at comparable or better yields than obtained with other gases. Excellent yields as well as good sulfur reduction in 30 minutes were obtained with sulfur dioxide admixed with nitrogen. As a matter of fact the sulfur reduction obtained with this mixture was only about 10% less than that obtained by treatment with air for twice the time interval. The yield, however, was 4 /2 times that obtained by the treatment with air.

These results demonstrate that sulfur dioxide was the most effective gas of all those tried for the desired purposes.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illustrate how the coke was prepared. More severe, higher temperature conditions are used in coking for chemicals.

Conditions in fluid coke)" reactor The advantages of the process of this invention will be apparent to those skilled in the art. The sulfur content is reduced to acceptable levels by an easily controlled economical process and satisfactory yields are maintained.

Several cycles of treatment with sulfur dioxide can be employed, if desired.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

l. A process for desulfurizing and increasing the density of fluid coke particles containing a high percentage of sulfur, said particles having been produced by contacting a heavy petroleum oil coking charge stock at a coking temperature with a body of coke particles maintained in the form of a dense, turbulent, fluidized bed in a reaction zone, wherein the oil is converted to product vapors and carbonaceous solids are continuously deposited on the coke particles, removing product vapors from the coking zone, heating a portion of the coke particles from the coking zone in a heating zone to increase the temperature of said fluidized particles, returning a portion of the heated coke particles from the heating zone to the coking zone and withdrawing product particles which comprises the steps of contacting the product coke particles with a sulfur dioxide containing gas at a temperature in the range of 2000 to 2900 F.

2. The process of claim 1 in which the fluid coke being treated has a sulfur content in the range of 4 to 12 Weight 3. The process of claim 2 in which the contacting with sulfur dioxide is carried out for a period of from 15 minutes to 6 hours.

4. The process of claim 3 in which the sulfur dioxide is admixed with a diluent gas, the mole of the sulfur dioxide is in the range of 5-100%.

5. The process of claim 4 in which the diluent gas is nitrogen.

6. The process of claim 5 in which about 20 vol. percent sulfur dioxide and vol. percent of nitrogen are utilized.

7. A process for desulfurizing and increasing the density of fluid coke particles containing a high percentage of sulfur, said particles having been produced by contacting a heavy petroleum oil coking charge stock at a coking temperature with a body of coke particles maintained in the form of a dense, turbulent, fluidized bed in a reaction zone, wherein the oil is converted to product vapors and of contacting the product coke particles with a sulfur dioxide containing gas at a temperature in "the range of 2200 to 2700 .F. for a time interval of from 30 minutes 3 to four-hours, the sulfur dioxide containing gas having,

5- from 5 to 100 mole percent sulfur dioxide.

No references cited. 

7. A PROCESS FOR DESULFURIZING AND INCREASING THE DENSITY OF FLUID COKE PARTICLES CONTAINING A HIGH PERCENTAGE OF SULFUR, SAID PARTICLES HAVING BEEN PRODUCED BY CONTACTING A HEAVY PETROLEUM OIL COKING CHARGE STOCK AT A COKING TEMPERATURE WITH A BODY OF COKE PARTICLES MAINTAINED IN THE FORM OF A DENSE, TURBULENT, FLUIDIZED BED IN A REACTION ZONE, WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS SOLIDS ARE CONTINUOUSLY DEPOSITED ON THE COKE PARTICLES, REMOVING PRODUCT VAPORS FROM THE COKING ZONE, HEATING A PORTION OF THE COKE PARTICLES FROM THE COKING ZONE IN A HEATING ZONE TO INCREASE THE TEMPERATURE OF SAID FLUIDIZED PARTICLES, RETURNING A PORTION OF THE HEATED COKE PARTICLES FROM THE HEATING ZONE TO THE COKING ZONE AND WITHDRAWING PRODUCT PARTICLES WHICH COMPRISES THE STEPS OF CONTACTING THE PRODUCT COKE PARTICLES WITH A SULFUR DIOXIDE CONTAINING GAS AT A TEMPERATURE IN THE RANGE OF 2200* TO 2700* F. FOR A TIME INTERVAL OF FROM 30 MINUTES TO FOUR HOURS, THE SULFUR DIOXIDE CONTAINING GAS HAVING FROM 5 TO 100 MOLE PERCENT SULFUR DIOXIDE. 